The autopropulsers of the invention are inspired in movement by aquatic animals which have been studied from the cinematic and energetic point of view by Lighthill in the article "Aquatic Animal Propulsion of High Hydrodynamic Efficiency" Journal of Fluid Mechanics, 1970, Vol. 44, part 2, pages 265-301. According to this article, the movement of aquatic animals which assure their proper propulsion are classified in two types:
A. movement of the caudal fin which is a movement at the stern of a flexible wall in contact with water on its two faces and travelled over by a progressive wave towards the rear; PA1 B. undulation in the form of a progressive wave of the skin of the aquatic animal. This is a movement of the same type as that preceding but one face only of the flexible wall is in contact with the water.
The autopropulser of the invention is related to the second type. It comprises essentially a flexible and elastic envelope of generally streamlined form endowed with flexural elasticity and means for applying movement to different points of this envelope of the same nature and out of phase with respect to one another such that the tangent of the envelope at each point conforms to the tangent to the profile of a transverse progressive wave in the water. The surface of the flexible envelope thus conforms itself to the surface of the progressive wave in the water.
In order to effect the desired movement of the envelope, the invention utilizes artificial muscles as described in French patent 2,076,778 of January, 1970 in the name of the present Applicant. One such artificial muscle is constituted by an envelope having a flexible and elastic wall in the form of a cylinder or more generally of an elongated surface of revolution and by two non-extensible filametry networks situated on said surface. The two filamentary networks can be attached to one another or not at their crossing points and they have the form of helixes or of pseudo-helixes of opposite direction wound on said elongated surface of revolution, the assembly forming a deformable trellis around this surface.
If the angle of the tangent to the helixes with respect to the axis of the cylinder or more generally the angle of the tangents to the pseudo-helixes or loxodromies with the generatrix of the surface of revolution is less than a certain critical value, increase in the volume of the envelope due to a pressure increase causes a shortening of its length and the enevelope functions as an ordinary muscle such as a biceps.
The preceding patent also describes a toroidal muscle constituted in analogous fashion to the muscle described hereinabove, that is to say, it shortens itself in length by expanding under the effect of the pressure; also contemplated is a toroidal muscle constituted in analogous manner but functioning in opposite sense, that is to say, it is elongated in length while becoming narrower under the effect of the pressure.